I am not aware that this is unlawful: what makes someone somewhere else think it might be?

We regularly see instances where we are asked to give undertakings to pay a landlord's costs whether the matter is completed or not. In such circumstances, we require our client (intending tenant) to deposit money with us to enable us to meet that undertaking.

I was not suggesting it was unlawful, just wondering if it was contrary to recommended practice. If it is not, what control does the non-client have if, for example, the solicitor does not get on with the job?